These Specialized stem shims are for mounting specific stem types to a specified Future Shock. There are two versions. One, the Specialized#S234800001, is for upgrading/mounting an S-Works Future stem on a 2023-present compatible Future Shock of specified bikes. The second, # S199900023, is for mounting a standard 1⅛" stem on the 2020-present Future Shock of specified bikes. These are not recommended or designed for any other use. The list of compatible bikes for each version can be quite long, please refer to the Specialized website for specific model listings.